1. Field of the Invention
The present invention relates generally to measuring apparatus. In particular, the present invention relates to an apparatus for measuring the length of fiber optic being deployed in an underwater environment or the like.
2. Description of the Prior Art
The military annually deploys several thousand miles of fiber optic cable underwater for use with communications systems. The underwater surface upon which the fiber optic cable is deployed is often not flat and may include craters, canyons, and even a vast chasm within which the fiber optic cable must be deployed.
When fiber optic cable is deployed in an underwater environment, there is a requirement that the cable follow the contour of the ocean floor, otherwise there may be excessive strain on the cable due to ocean currents when, for example, the cable is deployed within an underwater canyon. This excessive strain may eventually cause breakage of the fiber optic cable disrupting critical military communications systems. In addition, when excessive fiber optic cable is deployed over a given length of the ocean floor, twists and kinks may result in the cable being deployed.
There is available apparatus which will provide accurate contour measurements of the ocean floor. Using conventional and well known digital processors the length of fiber optic cable required for deployment to traverse a given distance across the ocean floor may then be calculated. However, when deploying cable from a cable reel, apparatus which are used to measure the length of the cable being deployed, such as pinch rollers, often provide inaccurate cable length measurements due to, for example, slippage of the cable passing through the pinch rollers and variations in the diameter of the fiber optic cable being deployed. This, for example, may result in a fiber optic cable being deployed under tension across a canyon which, in turn, may lead to breakage of the cable.
As is best illustrated by FIG. 1, prior art apparatus for monitoring the length of fiber optic cable being deployed comprised a pair of pinch rollers, a shaft encoder having one of the pinch rollers mechanically coupled thereto and a digital signal processor electrically connected to the shaft encoder. As the cable is being deployed the pinch rollers will rotate in the directions indicated and the shaft encoder being responsive to the rotation of the upper pinch roller will provide a pulse train with each pulse indicating that one inch of fiber optic cable has been deployed. The digital signal processor then receives the pulse train and in response to the pulse train calculates the length of fiber optic cable that has been deployed. This prior art cable deployment measuring apparatus also includes trip wires positioned at precise locations along the length of the cable with the first trip wire being positioned at, for example, one thousand forty seven feet and the second trip wire being positioned at two thousand thirty eight feet.
The trip wires, in turn, interface with the digital signal processor and provide an accurate reading of cable deployment by resetting an internal counter within the digital signal processor to the exact locations of the trip wires. Thus, when one thousand forty seven feet of fiber optic cable has been deployed the first trip wire attached to the cable will reset the counter within the digital signal processor to a value of one thousand forty seven.
This prior art cable deployment monitoring system in addition to providing inaccurate cable length measurements is a complex and expensive monitoring system which uses multichannel digital input/output interface circuits to connect the monitoring means, that is the encoder and the trip wires to the digital signal processor.
With the above and other disadvantages known to prior art cable length measuring apparatus the present invention was conceived and one of its objects is to provide a cable length measuring apparatus which will measure the length of fiber optic cable as the cable is being deployed in an underwater environment.
It is another object of the present invention to provide a relatively simple and inexpensive yet very accurate cable length measuring apparatus.
Various other objects and advantages of the present invention will become apparent to those skilled in the art as a more detailed description of the invention is set forth below.